Reflectivity is a measurement of the fraction of incident light (electromagnetic power) that is reflected at an interface between two materials. Reflectivity is a positive real number and equal to the square of the reflection coefficient (a complex number), which measures the fraction of the electric field reflected. The reflectivity of a material layer can vary with both incident angle and wavelength of the light incident on a material layer. Thus, to fully characterize the reflectivity of a material layer for a specific wavelength, reflectivity measurements should be taken at a variety of different incident angles. Fully and accurately characterizing the reflectivity of a material layer can be a time consuming process.